1. Field of the Invention
The present invention relates to a fuel supply control system for an internal combustion engine.
The present invention relates more particularly to a fuel supply control system wherein the fuel supply is cut off when the engine is decelerated from a first predetermined value and is resumed when the engine is further decelerated to a lower speed through a second predetermined value.
2. Description of the Prior Art
A conventional fuel supply control system installed in an internal combustion engine of an automotive vehicle cuts off the fuel supply during deceleration of the vehicle when fuel is generally not necessary for the engine, thus saving a considerable amount of fuel and maintaining an appropriate air-to-fuel ratio.
In this case, the conventional fuel supply control system does not cut off the fuel supply without reason but cuts off the fuel supply only when the speed of engine rotation, and thus the vehicle speed, drops from above a first predetermined value. Thereafter, the fuel supply is restored when such deceleration ends, or when the vehicle speed drops from the first predetermined value to a second predetermined value. Consequently, fuel supply cutoff can be prevented at a region of low vehicle speed and low engine rotation speed below the second predetermined value which might otherwise cause the engine to stall and hunting can also be prevented by the control of the fuel supply cutoff.
However, such a conventional fuel supply cutoff system has the problem that the fuel supply is resumed in the same way in response to the vehicle decelerating to arrive at the second predetermined value when the engine rotation speed decreases slowly while an accelerator pedal is slowly released to rotate the engine through a driving wheel for engine braking. The fuel supply is also resumed when the engine rotation speed drops abruptly during depression of the accelerator pedal and the transmission is in neutral so the vehicle is under no load. The fuel supply is also resumed when the vehicle is stopped by the sudden application of the brake pedal, so that during a delay between the resumption of fuel being supplied to the engine and the engine responding to the fuel, the engine rotation drops to a very low speed.
Consequently, in order to prevent the engine from stalling after a sudden depression of the brake pedal and a sudden release of the accelerator pedal, a second predetermined value is specified at which the fuel supply is resumed at much higher engine rotation speed than the value at which the engine would stall when the rotation speed is reduced slowly under the engine braking.
However, in such a case described above an unnecessary amount of fuel is consumed so that in the conventional fuel supply cutting off and recovery system there is a need for improving the fuel consumption.